The present invention relates to an ignition control system for an internal combustion engine and more in particular to a method and an apparatus for controlling the ignition timing of an internal combustion engine so as to operate the engine under the condition adapted to produce its maximum torque under a given fuel supply.
In one conventional control system, the ignition timing of the internal combustion engine has been controlled under what is called a programmed control, in which the ignition timing is controlled to meet predetermined characteristics depending on the engine operating conditions. Also, it is well known to use, as parameters for changing the ignition timing, the number of engine revolutions and the intake vacuum pressure of a fuel system. In such a control system, it would require many complicated programs if the control is to achieve an optimum ignition timing under any possible operating conditions and such a control is virtually impossible to obtain. It is also difficult to cope with the differences in engine structure and fuel properties to meet the ever-changing environmental conditions. For these reasons, the programs now employed for such purposes are limited to simple ones only using main parameters of operating conditions.
As a result, the engine may be operated at an ignition timing far from the optimum ignition timing, so that fuel consumption is unsatisfactory. In order to solve this problem, it has been suggested that more complicated programs be stored in a digital memory and selectively read out in accordance with the parameters of the operating conditions for controlling the ignition timing. Such a system, in spite of its advantage of high control accuracy, would be high in cost if it should be applicable to all possible situations. Another disadvantage of that system is the inability thereof to cope with the above-mentioned variations of fuel, environmental conditions and engine mechanisms or changes thereof with the lapse of time.
Another method for adjusting the ignition time wherein the fact that knocking or abnormal sound of an engine occurs due to an improper ignition timing is taken into consideration and is disclosed in the Japanese Patent Application No. 25511/76, published for public inspection on Oct. 8, 1976. This method, however, has disadvantages in that the ignition timing control is adversely affected by the surrounding noises, thus making it difficult to correct slight displacement from the optimum point of ignition timing.